Along with entries from 17 other teams, the sensor will be examined in lab trials over the next three months for its accuracy in measuring ocean water acidification. The top contenders will move to coastal and ocean trials in 2015 in the international competition for $2 million in prizes, which will be awarded to the most accurate and affordable sensors.

The competition, one of several sponsored by the XPRIZE organization to encourage solutions to global challenges, aims to spur development of new sensors to measure the acidification of ocean waters resulting from higher levels of atmospheric carbon. The National Oceanic and Atmospheric Administration notes that the ocean absorbs about a quarter of the carbon dioxide released into the atmosphere, which is changing the chemistry of seawater and affecting shellfish, fisheries, and coral reefs and other marine ecosystems.

However, according to the XPRIZE Foundation, current pH sensor technologies are too costly, imprecise, or unstable to provide sufficient knowledge on the state of ocean acidification.

One of the keys is that such sensors must be able to withstand the pressures in the ocean depths.

“When we first developed our sensor about five years ago, it appeared that no one else had ever measured pH under high pressure,” Sastry said. “At least, when we started, we didn’t find anything in the literature.

“To my knowledge, the measurements we made were the first of their kind.”

Measuring pH in processed foods is an important step in the research behind high-pressure food processing, currently about a $3 billion segment of the food market.

“With high-pressure food processing, we’re not exactly sure why it works in some cases,” Sastry said. “One of the hypotheses was that when you squeeze a food hard enough (by applying high pressure in an enclosed environment), you dissociate the hydrogen ions and create a more acid environment, which kills bacteria more easily.

“When you depressurize and come back to atmospheric pressure, all that acidity goes away instantaneously. It’s a pretty neat thing.”

To test the theory, researchers needed a pH sensor that could monitor a food’s acidity during high-pressure processing, not just beforehand and afterward. Standard pH meters have glass components that shatter under such conditions.

“So, the first thing was to make the sensor soft and pliable, so it could withstand the pressure,” Sastry said. “When we did that, we tried different types of typical pH sensors -- iridium, iridium oxide, all kinds of other sensors -- that we tried to adapt to high-pressure needs.

“But the big problem was that they didn’t give the same reading twice. Once we pressurized them, brought them back to atmospheric pressure, then pressurized them a second time, they didn’t give us the same result.”

Finally the team came up with a solution.

“One day it just kind of occurred to us to use another method to determine pH, and lo and behold, it worked,” he said.

Sastry and postdoctoral researcher Chaminda Samaranayake published their work in the Journal of Physical Chemistry in 2010, and their sensor and the method they devised were patented in 2012.

A representative from the XPRIZE Foundation saw the work and asked Sastry’s team to enter the competition earlier this year.

The pH sensor Sastry’s lab developed was created to withstand the extremely high pressures used in high pressure food processing, up to 87,000 pounds per square inch.

“High-pressure food processing uses pressure about 10 times the pressure at the bottom of the ocean,” Sastry said. “So, we’re confident our sensor will work fine under deep ocean conditions.”

However, the team had some extra legwork to do to adapt the sensor for measuring ocean water. First, they had to adapt the technology to allow water to flow in and out of the sensor -- something that isn’t necessary in a high-pressure food processing chamber, Sastry said. The team also had to develop a power source for the sensor.

“That introduced a whole new challenge,” Sastry said. “We now had to put a battery pack and a data logger inside a custom-made cylinder that could go under the ocean and power our sensor.”

The team started working on the project this spring and completed it in the first week of September. Brian Heskitt, a research associate who helped develop the sensor, traveled to California last week to train the competition’s staff on how to operate it.

Sastry expects to find out in January if the Ohio State sensor advances to the next phase of the competition.